Process for the preparation of bridged clays, clays prepared by said process, and uses for said clays

ABSTRACT

In a process for the preparation of bridged clays, a mixture of an aqueous solution of at least one metal hydroxide and aqueous clay suspension is subjected to dialysis. Said clays are suited for use as catalysts or as supports for catalysts for the conversion of paraffinic or olefinic hydrocarbons.

The present invention relates to a process for the preparation ofbridged clays, clays prepared by said process, and uses for said clays.

Some clays have an expandable network structure. They have the propertyof being able to adsorb especially water between the individual sheetsof which they are made up. This is true especially of themontmorillonite group of clays. These clays have a structure which maybe defined, in a simplified manner, as a three-layer structurecomprising two single layers of SiO₄ tetrahedrons and a dioctahedral ortrioctahedral intermediate layer. Cohesion between the layers is assuredby the fact that the apical oxygen atoms are coordinated. The siliconatoms of the tetrahedrons may be partly replaced by aluminum atoms.

Similarly, in the octahedrons of the AlX₆ (X=O, OH) intermediate layer,the aluminum atoms may be partly replaced by magnesium or iron atoms.Iron-bearing montmorillonites, called nontronites, are known in whichthe octahedral layer is formed entirely of iron octahedrons, the chargeof the sheet being the result of substitutions at the level of thetetrahedral layers. Saponite, a trioctahedral clay (magnesium octahedrallayer), has a charge due to substitutions at the level of the silicictetrahedral layers.

It is well known that the specific surface of a support is a veryimportant factor in catalysis, and because of their property of beingexpandable, these clays might be used as catalysts or supports forcatalysts, especially for the conversion of hydrocarbons. However, onceexpanded, in other words, after having adsorbed water between theirindividual sheets, these clays have the drawback of losing theirexpanded character when heated to 100° C., and consequently of notretaining the increase in specific surface which may result from theirexpansion.

It should be noted that the state of expansion of a clay is defined bythe intersheet spacing and the basal spacing, which are measured byx-ray diffraction.

As its name implies, the intersheet spacing is the spacing between twosheets. In the unexpanded state of the dried clay, it is zero.

The basal spacing, represented by the symbol d₀₀₁, is defined as the sumof the thickness of a sheet and the intersheet spacing.

In the case of montmorillonite, the thickness of a sheet is 9.6 angstromunits. In the expanded state, the intersheet spacing may exceed about 10angstrom units, and the basal spacing may therefore exceed about 20angstrom units.

With a view to using expanding clays as catalyst supports or ascatalysts, it has been sought to obtain clays having a maximum basalspacing that can be maintained when the clay is subjected to a heattreatment.

Thus it has been found that pillars or bridges can be inserted betweenthe clay sheets to obtain clays which hereinafter will be referred to as"bridged clays".

One well-known method consists in introducing between the clay sheetsbridges formed by oligomers of a metal hydroxide, and in particular ofan aluminum hydroxide.

This method, described specifically in an article by Lahav, U. Shani andJ. Shabtai which appeared in CLAYS AND CLAY MINERALS, volume 26 (1978),No. 2, pages 107 to 115, consists in contacting an oligomer of aluminumhydroxide with an aqueous suspension of montmorillonite. The methoddescribed makes it possible to obtain a basal spacing of about 18angstrom units. The article points out that the hydroxyaluminum solutionobtained by reaction of soda with aluminum chloride must be aged beforeit is brought into contact with the clay suspension. This processtherefore is rather time-consuming. Moreover, the concentration of theclay suspensions used is very low. It ranges from 50 to 200 mg per literof suspension, equivalent to from 0.005 to 0.02 weight percent. Thismethod therefore makes it necessary to handle large volumes ofsuspension, which of course is a disadvantage.

The article further points out that it is preferable to use a relativelyhigh OH⁻ /Al³⁺ ratio, namely, 2.33. Now when an OH⁻ /Al³⁺ ratio on theorder of 3 is used, there is the risk of uncontrolled crystallization ofbayerite and/or gibbsite, Al(OH)₃, outside the sheets, which is anadditional disadvantage.

The method described in that article thus is afflicted with severaldrawbacks.

Another method, described in French Pat. No. 2,394,324, consists incontacting clay with a solution of aluminum chlorohydroxide called"chlorhydrol". This method likewise entails drawbacks since clay and"chlorhydrol" must be brought into contact with each other at arelatively high temperature (the patent mentions temperatures on theorder of 70° C.), and aging is likewise required.

The invention proposes a new method of preparing "bridged clays" whichis not afflicted with the drawbacks of the prior art outlined above.

To this end, disclosed herein is a process for the preparation ofbridged clays which is characterized in that a mixture of an aqueoussolution of at least one metal hydroxide and an aqueous clay suspensionis subjected to dialysis.

Aqueous solution of at least one metal hydroxide means a solutioncontaining OH⁻ and M^(x) ions of at least one metal in which the OH⁻/M^(x) ratio is such that the precipitation threshold of the hydroxideis not reached.

In accordance with the invention, the hydroxide may be selected from thegroup comprising the hydroxides of the elements of groups IIB, IIIB,IVB, VB, VIB, VIIB, VIII, IA, IIA, IIIA, IVA, VA and VIA of the periodictable of the elements.

In the process in accordance with the invention, the hydroxide may beobtained by the action of a base on a metal-salt solution in which themetal is present as a cation, or of an acid on a metal-salt solution inwhich the metal is present as an anion.

The mixture of the solution of at least one hydroxide of a metal and theclay suspension may be produced in different ways, namely:

By preparing the hydroxide solution, for example, by the action of abase on a salt, and then adding the solution so obtained to the claysuspension;

by adding to the clay suspension a solution of the metal salt and thenadding a base solution; or

by adding to the clay suspension simultaneously a solution of the metalsalt and a base.

In other words, the hydroxide solution may be prepared before it ismixed with the clay suspension, or by adding the precursors of thehydroxide solution to the clay suspension.

The hydroxide solution may also be obtained from certain compounds whichhydrolyze spontaneously, without it being necessary to add a base; forexample, from the oxychlorides of zirconium, vanadium, molybdenum orrhenium.

One of the important parameters in the process of the invention is theOH⁻ /M^(x) ion ratio in the hydroxide solution, where x defines thedegree of oxidation of the metal.

When x=I, the OH⁻ /M^(I) ratio may range from 0.2 to 1, and preferablyfrom 0.2 to 0.8, and more particularly from 0.3 to 0.7.

When x=II, the OH⁻ /M^(II) ratio may range from 0.2 to 2, and preferablyfrom 0.4 to 1.8, and more particularly from 0.5 to 1.4.

When x=III, the OH⁻ /M^(III) ratio may range from 0.3 to 3, andpreferably from 0.6 to 2.4, and more particularly from 0.8 to 1.8.

When x=IV, the OH⁻ /M^(IV) ratio may range from 0.4 to 4, and preferablyfrom 0.8 to 3.6, and more particularly from 1 to 2.8.

In the process of the invention, the concentration in the mixture of theclay suspension and the hydroxide solution of the ion of the metal usedto form the metal-oxide pillars should be sufficiently high to result inthe formation of metal-oxide pillars yet not so high that too much metaloxide is inserted between the clay sheets, which would impair theporosity of the clay.

Said concentration, expressed in milliequivalents (meq) of the ion ofthe metal involved per gram of clay, may range from 6 to 60, andpreferably from 10 to 30.

The clay concentration in the final mixture, that is to say, aftermixing of the hydroxide solution and the initial clay suspension, shouldbe sufficiently high to obviate the handling of large volumes ofmixture, yet not excessively high since too high a clay concentration inthe mixture would make the latter difficult to handle.

The clay concentration in the final mixture may range from 0.1 to 4weight percent, and preferably from 0.8 to 1.5 weight percent, forexample.

The clays which may be used in the process of the invention may beselected from the group formed by the swelling clays (smectites, whethernatural or produced by hydrothermal synthesis).

The final step of the process in accordance with the invention consistsin subjecting the mixture of the solution of at least one metalhydroxide and the clay suspension to dialysis.

The dialysis may be carried out by placing said mixture in a containerformed by a semipermeable membrane selected from the group comprisingthe membranes based on regenerated cellulose, or by any othersemipermeable membrane.

The container is then immersed in water, preferably demineralized wateralthough any kind of water (distilled water, tap water, etc.) may beused as its ionic strength will be lower than that of the watercontained in the dialysis membrane.

The operation may be carried out discontinuously or continuously. In thelatter case, the container is placed in a stream of water.

The dialysis operation may be carried out at ambient temperature but canbe accelerated by raising the temperature of the water. The temperatureis limited by the boiling temperature of the water at the pressure atwhich the operation is performed.

The clays prepared by the process in accordance with the inventionpossess very good thermal stability and preserve their basal spacingwhen they are brought to a high temperature. They are therefore suitablefor use as catalyst supports and as catalysts, particularly in theconversion of hydrocarbons.

They are especially well suited for use as catalysts or catalystsupports in the isomerization of paraffinic or olefinic hydrocarbons orin the cracking of these hydrocarbons, optionally in the presence ofhydrogen.

Thus at least one of the elements from groups IB, IIB, IIIB, IVB, VB,VIB, VIIB, VIII, IA, IIA, IIIA, IVA, VA and VIIA of the periodic tableof the elements may be deposited on these clays.

The six examples which follow will serve to illustrate the inventionwithout limiting it.

The five figures which accompany the present specification are explainedin these examples.

FIGS. 1, 2a and 2b are x-ray diffraction charts of control clays and ofclays prepared according to this invention.

FIG. 3 schematically illustrates apparatus used for testing the claysprepared according to this invention.

FIG. 4 is a chromatography chart showing the isomerization activity ofclays prepared according to this invention.

EXAMPLE 1

This example relates to the preparation of bridged clays A1, A2, A3, A4,A5, A6, A7, A8, A9, A10, A11, A12, A13 and A14 by the process of theinvention as well as of control bridged clays TA2, TA4 and TA6 by anallied process which did not, however, include the final dialysisoperation.

The starting material was a montmorillonite, which was saturated withsodium ions, Na⁺, by being treated repeatedly with a normal aqueoussolution of sodium chloride.

The excess sodium chloride was eliminated by centrifugation. The claywas washed several times with demineralized water, centrifugation beingeffected after every wash.

The fraction whose particle size was 2 microns or less was separated bydecantation, the fraction of a particle size above 2 microns beingeliminated.

From said clay fraction, aqueous suspensions S1 and S2 containing 2.5and 4.16 weight percent clay, respectively, were prepared.

There were further prepared:

An aqueous solution I of aluminum chloride, AlCl₃.6H₂ O;

an aqueous solution II of chromium chloride, CrCl₃.6H₂ O; and

an aqueous solution III of sodium hydroxide, NaOH.

The three solutions I, II and III had a molar concentration of 0.2.

Solution III was added to solution I and/or to solution II in varyingamounts gradually, with continuous agitation, so as to avoid theformation or appearance of turbidity. In this way, different hydroxidesolutions of varying OH⁻ /Al³⁺ or OH⁻ /Cr³⁺ or OH⁻ /Cr³⁺ plus Al³⁺ plusAl³⁺ ratios were obtained.

The different hydroxide solutions obtained were then mixed in varyingamounts, with agitation, with a certain amount of suspension S1 or S2.

In this way, mixtures containing the metal or metals in varyingconcentrations were obtained.

For preparation of the control clays TA2, TA4 and TA6, some of themixtures obtained were simply washed with demineralized water.

For the preparation of clays by the process of the invention, themixtures obtained were placed in a pocket formed of a semipermeablecellulose membrane having an average porosity of 24 angstrom units,marketed under the trademark VISKING by Medicell International Ltd.

The pocket was placed in 10 liters of demineralized water for a periodof 24 hours. The operation was repeated four times.

Following this dialysis operation, samples were taken from the productsobtained by the two procedures, and these samples were examined by x-raydiffraction.

The suspensions were centrifuged, and the various products obtained weredried by lyophilization.

The conditions of preparation of the bridged clays obtained and theirbasal spacing, measured by x-ray diffraction, are given in Table 1 whichfollows.

                                      TABLE 1                                     __________________________________________________________________________     Clay pre-                                                                        Amount of solution or suspension used in the preparation of the clay          (in milliliters) Solution IIISolutionSolution IIIS.sub.1suspensionClay        lay suspension S.sub.2      OH.sup.- /M.sup.3+ ion ratio                                                        Concentration, in meq, per gram of                                           clay                                                                                   ##STR1##                                                                               Basal spacing          pared                                                                             (1)  (2)  (3)  (4)   (5)   (6)   (7)     (8)      (9)                     __________________________________________________________________________    Al  333  0    266  400   0     0.8   20      --       19                      A2  333  0    333  400   0     1.0   20      --       19                      TA2 333  0    333  400   0     1.0   20      --       16.2                    A3  333  0    400  400   0     1.2   20      --       19                      TA3 333  0    400  400   0     1.2   20      --       16.2                    A4  333  0    466  400   0     1.4   20      --       18.2                    TA4 333  0    466  400   0     1.4   20      --       17.3                    A5  333  0    533  400   0     1.6   20      --       19.1                    A6  333  0    566  400   0     1.7   20      --       18                      TA6 333  0    566  400   0     1.7   20      --       12.4                    A7  333  0    666  400   0     2.0   20      --       19.5                    A8  166.5                                                                              0    333  0     240   2.0   10      --       18                      A9  166.5                                                                              0    383  0     240   2.3   10      --       17.9                    A10 166.5                                                                              0    416  0     240   2.5   10      --       17.9                    A11 0    333  466  400   0     1.4   20      --       17.6                    A12 0    333  666  400   0     2.0   20      --       19                      A13 230  100  333  400   0     1.0   20      30       17.6                    A14 165  165  333  400   0     1.0   20      50       17.2                    __________________________________________________________________________     (1) Solution of AlCl.sub.3.6H.sub.2 O, 0.2 molar.                             (2) Solution of CrCl.sub.3.6H.sub.2 O, 0.2 molar.                             (3) Solution of NaOH, 0.2 molar.                                              (4) Suspension, 2.5 weight percent.                                            (5) Suspension, 4.16 weight percent.                                         (6) In the metal hydroxide solution (in the case of a mixed Al and Cr         solution).                                                                    (7) Concentration of the metal ion or ions (in the case of a mixed Al and     Cr solution) in the mixture of hydroxide solution and clay suspension.        (8) In the case of a mixed Al and Cr solution.                                (9) After drying at ambient temperature.                                 

It is apparent from Table 1 that the basal spacing of the clays preparedby the process of the invention is greater than that of the claysprepared by a process without dialysis. Comparison of the clays A6 andTA6 will bring this out particularly well.

The x-ray diffraction spectrum of the clays A6 and TA6, dried at ambienttemperature, is given in the accompanying FIG. 1.

It will be noted that the basal spacing of clay A6 is greater than thatof clay TA6 and that the line of clay A6 is narrower and more intensethan that of clay TA6. This indicates that the aluminum hydroxy layerinterposed between the sheets is very much better organized in clay A6than in clay TA6.

The clays so prepared were then subjected to different heat treatments.After each treatment their basal spacing was measured. The resultsbefore and after the heat treatment are presented in Table 2 whichfollows.

                                      TABLE 2                                     __________________________________________________________________________            Basal spacing in angstrom units                                       Before  Heat-treating conditions                                                 heat 2 hours                                                                             2 hours                                                                             1 hour                                                                              1 hour                                                                              1 hour                                                                              1 hour                                  Clay                                                                             treatment                                                                          at 100° C.                                                                   at 200° C.                                                                   at 300° C.                                                                   at 400° C.                                                                   at 500° C.                                                                   at 550° C.                       __________________________________________________________________________    A1 19               18.1        17.1                                          A2 19               18.1        17.1                                          TA2                                                                              16.2             11.2        9.7                                           A3 19               18          17                                            TA3                                                                              16.2             11.2        9.4                                           A4 18.2       17.8        17.3        16.9                                    TA4                                                                              17.3 17    12.3        9.7         9.7                                     A5 19.1             17.6        16.3                                          A6 18                                                                         TA6                                                                              12.4                                                                       A7 19.5             17          16                                            A8 18               17.3        16.9                                          A9 17.9             17.3        16.8                                          A10                                                                              17.9             17.2        16.3                                          A11                                                                              17.6             16.4                                                      A12                                                                              19   18          17                                                        A13                                                                              17.6             14.7                                                      A14                                                                              17.2             14.5                                                      __________________________________________________________________________

As may be seen from Table II, the basal spacing of of the clays preparedby the process of the invention is reduced but slightly withtemperature, which of course is an advantage when these clays are usedas catalyst supports or as catalysts.

This is not the case with the control clays prepared by a processwithout dialysis.

Shown in FIGS. 2a and 2b by way of example are the peaks obtained byx-ray diffraction for the clays A4 and TA4, respectively, from which itis apparent that the basal spacing of clay TA4 is reduced by heattreatment.

The specific surfaces of the various bridged clays were measured on thebasis of nitrogen adsorption isotherms obtained at the temperature ofliquid nitrogen by the BET method. The specific surfaces ranged from 200to 400 m² /g. The clays had first been degassed under vacuum at 300° C.for 16 hours.

The porosity distribution determined on the basis of nitrogen desorptionisotherms was binodal, with pores ranging in diameter from 40 to 50angstrom units and pores of a diameter between 10 and 20 angstrom units.

EXAMPLE 2

This example relates to the preparation of a bridged clay B by theprocess in accordance with the invention.

The starting material was a montmorillonite, which was treated as inExample 1, that is to say, exchange by means of sodium chloride, thenseparation of the fraction whose particle size was 2 microns or less.

To an aqueous suspension of this montmorillonite containing 2.5 weightpercent of the clay there was added 30 milliliters of an 0.2 molarsolution of zirconium oxychloride, ZrOCl₂. 130 milliliters of distilledwater was then added to give an aqueous suspension containing 0.5 weightpercent of clay.

The suspension was dialyzed by means of a membrane identical to thatused in Example 1 at the rate of 1 liter of demineralized water per gramof clay.

The dialysis water was replaced after 24 hours. A sample was taken aftereach dialysis for examination by x-ray diffraction.

The samples were dried at ambient temperature, then subjected todifferent heat treatments.

The results before and after heat treatment are presented in Table IIIwhich follows.

                  TABLE 3                                                         ______________________________________                                                   Basal spacing in angstrom units                                                 After 1 After 3   After 4                                                                             After 5                                  Treatment    dialysis                                                                              dialyses  dialyses                                                                            dialyses                                 ______________________________________                                        Drying at ambient                                                                          11.3    19.6      18.5  19                                       temperature                                                                   At 110° C.                                                                          11      16.4      16.1  16.4                                     At 400° C.                                                                          10      15.7      15.7  15.7                                     ______________________________________                                    

The influence of the dialysis is clearly apparent from this table. Thebasal spacing remains fairly high despite the heat treatment.

EXAMPLE 3

This example relates to the preparation of a bridged clay C by theprocess of the invention and of a control bridged clay TC by a processwhich does not include a final dialysis step.

The starting material was a montmorillonite fraction identical to thatused in Examples 1 and 2.

To an aqueous suspension of this montmorillonite, titanium sulfate,Ti(SO₄)₂, in an acidic solution was added at the rate of 33 mg oftitanium per gram of clay.

The final concentration of the clay suspension was 0.25 weight percent.A sample was taken and dried. This was the control clay TC.

The suspension was dialyzed as in Example 2 and samples were taken,treated and examined in the same manner.

The results are presented in Table 4 which follows.

                  TABLE 4                                                         ______________________________________                                               Basal spacing in angstrom units                                               Control                                                                       clay TC  Clay C after                                                           (without   one      two      three                                   Treatment                                                                              dialysis)  dialysis dialyses dialyses                                ______________________________________                                        Drying at                                                                              12.2       12.4     23.2     23                                      ambient                                                                       temperature                                                                   At 110° C.                                                                      Not        12.1     20       23.2                                             measured                                                             At 300° C.                                                                      Not        Not      Not      23.8                                             measured   measured measured                                         ______________________________________                                    

The influence of dialysis is clearly apparent from this table. The basalspacing remains fairly high despite the heat treatment.

EXAMPLE 4

This example relates to the preparation of a bridged clay D by theprocess of the invention and of a control bridged clay TD by a processwhich does not include a final dialysis step.

The starting material was a montmorillonite fraction identical to thatused in Examples 1, 2 and 3.

To an aqueous suspension of this montmorillonite containing 2.5 weightpercent of the clay, 20 meq of holmium per gram of clay was added in theform of holmium nitrate, Ho(NO₃)₃.6H₂ O, in aqueous solution.

The final suspension contained 1 weight percent of clay.

The suspension was dialyzed as in Example 3 and samples were taken,treated and examined in the same manner.

The x-ray diffraction pattern showed that the 001 lines become finerwith the number of dialyses and increases in intensity, which manifeststhe beneficial effect of dialysis on the regular arrangement of thesheets, which itself is due to the provision of the bridges.

Shown in table V which follows are the intensities of the 001 line at15.5 angstrom units as a function of the number of dialyses.

The intensities were measured on the basis of the x-ray diffractionpattern and multiplied by the number of shots per second.

                  TABLE 5                                                         ______________________________________                                                Intensity of 001 line multiplied                                              by the number of shots/sec                                                    Control                                                                       clay TD                                                                              Clay D after                                                             (without one      two    three                                      Treatment dialysis)                                                                              dialysis dialyses                                                                             dialyses                                   ______________________________________                                        Drying at 1,220    7,500    11,000 10,000                                     ambient                                                                       temperature                                                                   At 110° C.                                                                       680      2,680    2,800  Not measured                               At 300° C.                                                                       120      1,120    1,640  3,000                                      ______________________________________                                    

The influence of dialysis is clearly apparent from this table andpersists despite the heat treatment.

EXAMPLE 5

This example relates to the hydroisomerization and hydrocracking of acharge of normal decane with the aid of catalysts prepared from theclays of Example 1.

From the various clays of Example 1, catalysts containing 1 weightpercent platinum were prepared by impregnating the clays with an aqueoussolution of tetramineplatinum chloride, Pt(NH₃)₄ Cl₂.

After being dried at 110° C. for 16 hours, the products obtained werecalcined in air and then reduced by a hydrogen stream.

Catalysts which are referenced in Table 6 which follows were soobtained.

                  TABLE 6                                                         ______________________________________                                        Starting clay  Catalyst                                                       ______________________________________                                        A2             C2                                                             A3             C3                                                             A4             C4                                                             A7             C7                                                             A8             C8                                                             A9             C9                                                             A10            C10                                                            A11            C11                                                            A13            C13                                                            A14            C14                                                            ______________________________________                                    

A normal-decane hydroisomerization and hydrocracking test was then runwith each catalyst by placing a given amount of catalyst in a 5-mlreactor. A mixture of normal decane and hydrogen was then passed overthe catalyst at atmospheric pressure and at such normal-decane feed rateF_(o) at the top of the reactor that, with W representing the catalystweight, the W/F_(o) ratio was 518 kg/second/mole, the hydrogen/normaldecane ratio being 71 standard liters per liter.

The tests were run with the temperature being increased from 100° to300° C. to secure total conversion of the normal decane.

Successive checks were made, through gas-chromatographic analyses of thegases leaving the reactor, to determine

the temperature at which 20% conversion of normal decane was obtained;

the temperature at which the isomerization maximum was reached; and

the temperature at which 20% cracking was secured.

The amounts of catalyst used and the results of these tests arepresented in Table 7 which follows.

                                      TABLE 7                                     __________________________________________________________________________            Catalyst pre-                                                                 treating con-                                                                 ditions.        Temperature                                                   Oxidation and                                                                        Amount of                                                                              at which 20%                                                                         Isomerization                                                                        Temperature                                     calcination                                                                          catalyst conversion                                                                           maximum                                                                              at which 20%                            Test    temperatures                                                                         Weight                                                                            Volume                                                                             was obtained                                                                            Temp.                                                                             cracking was                            No.                                                                              Catalyst                                                                           in °C.                                                                        mg  ml   °C.                                                                           %  °C.                                                                        secured, °C.                     __________________________________________________________________________    1  C2   400    160 0.6  195    52 245 245                                     2  C3   400    200 0.5  190    55 232 231                                     3  C4   400    130 0.6  197    65 249 269                                     4  C7   400     85 0.5  200    55 252 230                                     5  C8   400    125 0.6  205    55 255 275                                     6  C9   400    200 0.5  231    50 281 330                                     7  C10  400    190 0.5  208    55 262 272                                     8  C11  400    186 0.6  192    58 227 227                                     9  C13  300    420 0.6  167    50 190 190                                     10 C14  300    420 0.6  147    55 172 172                                     11 C14  420    390 0.6  180    55 220 220                                     __________________________________________________________________________

As may be seen from Table 7, the bridged clays prepared by the processof the invention can be used to produce isomerization and crackingcatalysts which are efficient at relatively low temperatures.

These reactions will not occur when an unbridged clay containing 1weight percent platinum is used.

EXAMPLE 6

This example relates to the isomerization of a charge of butene-1 withthe aid of clays A1, A3, A5 and A7.

The apparatus diagrammed in FIG. 3 was used to carry out these tests.

Into a 25-ml reactor 1, 140 mg clay was placed. The reactor wasconnected through a line 2 to a three-way valve 3, which in turn wasconnected through a line 4 to a circulating pump 5, which in turn wasconnected to the reactor 1 through a line 6.

The reactor 1 and the lines 2, 4 and 6 thus formed a loop whose totalvolume was 1.3 liters and in which it was possible to

produce a vacuum by means of a line 7, a three-way valve 8 and a line 9connected to a vacuum pump (not shown);

take gas samples for analysis through line 7, the three-way valve 8 anda line 10 connected to a chromatograph (not shown); and

introduce a gas such as butene-1 through a line 11 provided with a valve12 and and connected to line 2.

The reactor was equipped with a heating system (not shown).

The tests were run in the following manner: After the clay had beenplaced in the reactor, the loop was degassed by means of the vacuum pump5, the reactor temperature being 250° C. When the pressure reached 10⁻⁶mm Hg, the vacuum circuit was isolated and the reactor temperature wasreduced to 100° C.

Butene-1 was then introduced into the loop in such an amount that thepressure was 40 mm Hg.

The circulating pump 5 was cut in and samples were periodically takenand analyzed by chromatography.

The results obtained are shown in FIG. 4.

It is apparent from FIG. 4 that the clays prepared by the process inaccordance with the invention have very good isomerizing activity.

We claim:
 1. A process for the preparation of bridged clays, comprisingsubjecting a mixture of an aqueous solution of at least one metalhydroxide and an aqueous clay suspension to dialysis.
 2. A processaccording to claim 1, wherein the clay is a natural or syntheticsmectite swelling clay.
 3. A process according to claim 1, wherein saidhydroxide is selected from the group formed by the hydroxides of theelements of groups IIB, IIIB, IVB, VB, VIB, VIIB, VIIIB, IA, IIA, IIIA,IVA, VA and VIA of the periodic table of the elements.
 4. A processaccording to claim 3, wherein the dialysis is carried out with the aidof a semipermeable membrane selected from the group consisting oforganic membranes.
 5. A process according to claim 3, wherein saidmembrane is selected from the group consisting of membranes based onregenerated cellulose.
 6. A process according to claim 3, wherein theconcentration of the metal ion of the hydroxide in the mixture of claysuspension and hydroxide solution, expressed in milliequivalents pergram of clay, ranges from 6 to
 60. 7. A process according to claim 6,wherein the concentration of clay in the mixture of clay suspension andhydroxide solution ranges from 0.1 to 4 weight percent.
 8. A processaccording to claim 3, wherein the concentration of clay in the mixtureof clay suspension and hydroxide solution ranges from 0.1 to 4 weightpercent.
 9. A process according to claim 3, wherein the degree ofoxidation of the metal M of the hydroxide is equal to IV and the OH⁻/M^(IV) ratio ranges from 0.4 to
 4. 10. A process according to claim 3,wherein the degree of oxidation of the metal M of the hydroxide is equalto III and the OH⁻ /M^(III) ratio ranges from 0.3 to
 3. 11. A processaccording to claim 10, wherein the metal of the hydroxide is at leastone metal selected from the group formed by aluminum, chromium andholmium.
 12. A process according to claim 11 wherein said membrane isselected from the group consisting of membranes based on regeneratedcellulose.
 13. A process according to claim 3, wherein the degree ofoxidation of the metal M of the hydroxide is equal to II and the OH⁻/M^(II) ratio ranges from 0.2 to
 2. 14. A process according to claim 3,wherein the degree of oxidation of the metal M of the hydroxide is equalto I and the OH⁻ /M^(I) ratio ranges from 0.2 to
 1. 15. A processaccording to claim 3, wherein the clay is a natural or syntheticsmectite swelling clay.
 16. A process according to claim 15, wherein theconcentration of clay in the mixture of clay suspension and hydroxidesolution ranges from 0.1 to 4 weight percent.
 17. A process according toclaim 15, wherein the concentration of clay in the mixture of claysuspension and hydroxide solution ranges from 0.8 to 1.5 weight percent.18. A process according to claim 15, wherein the concentration of themetal ion of the hydroxide in the mixture of clay suspension andhydroxide solution, expressed in milliequivalents per gram of clay,ranges from 10 to
 30. 19. A process according to claim 18, wherein theconcentration of clay in the mixture of clay suspension and hydroxidesolution ranges from 0.8 to 1.5 weight percent.
 20. A process accordingto claim 19, wherein the degree of oxidation of the metal M of thehydroxide is equal to I and the OH⁻ /M^(I) ratio ranges from 0.3 to 0.7.21. A process according to claim 19, wherein the degree of oxidation ofthe metal M of the hydroxide is equal to II and OH⁻ /M^(II) ratio rangesfrom 0.5 to 1.4.
 22. A process according to claim 19, wherein the degreeof oxidation of the metal M of the hydroxide is equal to III and the OH⁻/M^(III) ratio ranges from 0.8 to 1.8.
 23. A process according to claim22, wherein the metal of the hydroxide is at least one metal selectedfrom the group formed by aluminum, chromium and holmium.
 24. A processaccording to claim 19, wherein the degree of oxidation of the metal M ofthe hydroxide is equal to IV and the OH⁻ /M^(IV) ratio ranges from 1.0to 2.8.
 25. A process according to claim 15, wherein the concentrationof the metal ion of the hydroxide in the mixture of clay suspension andhydroxide solution, expressed in milliequivalents per gram of clay,ranges from 6 to
 60. 26. A process according to claim 25, wherein theconcentration of clay in the mixture of clay suspension and hydroxidesolution ranges from 0.1 to 4 weight percent.
 27. A process according toclaim 26, wherein the dialysis is carried out with the aid of asemipermeable membrane selected from the group consisting of organicmembranes.
 28. A process according to claim 26, wherein said membrane isselected from the group consisting of membranes based on regeneratedcellulose.
 29. A process according to claim 26, wherein the degree ofoxidation of the metal M of the hydroxide is equal to I and the OH⁻/M^(I) ratio ranges from 0.2 to 0.8.
 30. A process according to claim26, wherein the degree of oxidation of the metal M of the hydroxide isequal to IV and the OH⁻ /M^(IV) ratio ranges from 0.8 to 3.6.
 31. Aprocess according to claim 26, wherein the degree of oxidation of themetal M of the hydroxide is equal to II and the OH⁻ /M^(II) ratio rangesfrom 0.2 to
 2. 32. A process according to claim 26, wherein the degreeof oxidation of the metal M of the hydroxide is equal to I and the OH⁻/M^(I) ratio ranges from 0.2 to
 1. 33. A process according to claim 26,wherein the degree of oxidation of the metal M of the hydroxide is equalto II and the OH⁻ /M^(II) ratio ranges from 0.4 to 1.8.
 34. A processaccording to claim 26, wherein the degree of oxidation of the metal M ofthe hydroxide is equal to IV and the OH⁻ /M^(IV) ratio ranges from 0.4to
 4. 35. A process according to claim 26, wherein the degree ofoxidation of the metal M of the hydroxide is equal to III and the OH⁻/M^(III) ratio ranges from 0.3 to
 3. 36. A process according to claim35, wherein the metal of the hydroxide is at least one metal selectedfrom the group formed by aluminum, chromium and holmium.
 37. A processaccording to claim 26, wherein the degree of oxidation of the metal M ofthe hydroxide is equal to III and the OH⁻ /M^(III) ratio ranges from 0.6to 2.4.
 38. A process according to claim 37, wherein the metal of thehydroxide is at least one metal selected from the group formed byaluminum, chromium and holmium.
 39. A process according to claim 38,wherein said membrane is selected from the group consisting of membranesbased on regenerated cellulose.
 40. A clay prepared by the processaccording to one of claims 1 or
 26. 41. A catalyst comprising a clayaccording to claim
 40. 42. A catalyst consisting of a clay according toclaim
 40. 43. A catalyst according to claim 42, further comprising atleast one of the elements of the groups IB, IIB, IIIB, IVB, VB, VIB,VIIB, VIII, IA, IIA, IIIA, IVA, VA, and VIIA of the periodic table ofthe elements.
 44. A catalyst according to claim 43, wherein the elementwhich it comprises is an element from group VIII.
 45. A catalystaccording to claim 43, wherein the element from group VIII is platinum.46. A process according to any of claims 24, 34 or 30, wherein the metalof the hydroxide is at least one metal selected from the group formed byzirconium and titanium.